Hi All,
This is my first post here so please excuse any shortcomings
I had a very similar problem with a Moto G 3rd generation (model XT1541 from 2015) device, Android version 5.1.1.
After some digging I have discovered that the voltage on the USB OTG port of my phone was dropping from 5V to 0V upon connecting of the ThermApp camera.
This is what I was able to establish, I'll try to be as specific as I can:
1) The current sourcing capability of my Mogo G is well in excess of 150mA (verified by connecting a 33 Ohms resistor to the USB OTG port which meant the phone was sourcing about 160mA without a problem)
2) The ThermApp camera draws about 80mA on average, but it has short spikes of a much greater current demand
3) These spikes trigger the port's short circuit protection that cut off the power
I am guessing that because the Moto G 3rd gen has became water resistant (2nd gen wasn't) they have dramatically increased the "aggressiveness" of their USB OTG port's short circuit protection to also protect its pins from electrolytic damage under water.
It is bad for the metal pins to be powered under water, of course, so the less current flows through them under water the better..
It seems I have a length limit on the post, so I need to split it here, the rest I will post in the next one...